Getting Precise Stellar Parameters in PLATO’s first field

Getting Precise Stellar Parameters in PLATO’s first field PLATO science conference 24/25th Feb 2011 T. Granzer, K.G. Strassmeier, & M. Weber

A dedicated input catalog? • Dedicated photometric characterization survey in Strömgren uvbynw and H • Deliverables: (b-y), c1, m1,   Teff, [M/H], log g; Flux F(H) down to 13mag. • Constraints: bright limit 9.5, faint 16mag • First field (fixed) in southern hemisphere • Challenge: 2000 □2

Challenge: 2000 sq-deg • Super Wasp-South (SAAO), 8x11.1cm lens optics, FoV 7.8x7.8º,~35 pointings, filters ‘on demand’ (?) • OmegaCam@VST (Paranal): 2.6m Ritchey-Crétien, FoV 1x1º,~2000 pointings, ugriz&H • RoboTel (C. Armazones): 80cm, Cassegrain, 33.5 arcmin, ~7500 pts., full Strömgren and H set (plus UBVRI, ugriz). • RoboTel (C. Armazones): 80cm, Cassegrain, 33.5 arcmin, ~7500 pts., full Strömgren and H set (plus UBVRI, ugriz).

Robotel

LBT Mt.Graham 5min, seeing 0.8“ B-band NGC 891 RoboTel in Potsdam 20min, seeing 3.3“ V-band

Identical Instrumenton STELLA-1,1.2m, Izaña • 40 sec, on 5.8.2010 • 1.3´´ seeing 10´´ 1´´

Bochum-University/Antofagasta Observatory at base of Cerro Armazones ~50% seeing < 1” ~350 clear nights Image: R. Chini

Strömgren indices (b-y) for eff. Temperature m1=(v-b)-(b-y) for line blanketing c1=(u-v)-(v-b) for Balmer discontinuity For late-type (FGKM) stars (dwarfs), m1 is a good proxy for metallicity, c1 for log(g) The calibrations used for error analysis are from: Holmberg et al., A&A 475, 519 Ramirez & Melendez, ApJ 626, 446 Árnadóttir et al., A&A 521, A40

3-year survey? • 1300h/year h>30 • 85% clear nights • Moon: 3-5 days around full moon • Downtime <20% (STELLA) • Standards? (~20min/night) 11-17min/pointing

Photometric precision translates to 13.3-15.8 STELLA-1 (1.2m)! Including slewing/read-out overhead, effective exposuretimes in y are • 10.3-23.7 sec. (8 filters) • 20.1-40.7 sec. (6 filters) • 52.6-97.2 sec. (4 filters) ybv = 3.5-15 mmag, u = 8-30 mmag

…but only in the standard system varies slowly nightly Transformation to account for different filter curves (i, i) and atmospheric conditions (k’i, i) …determined by observation of standard fields, with errors k, , , .

Observe at high and low X (b-y) m1 c1  0.015 0.08 0.12  - 0.05 0.22 k’ 0.007 0.012 0.024  0.009 0.015 0.03 On STELLA-1, two observations in one night, each 20min at X=1.5 and X=1.05 …errors hold only for the standard field!

Reddening? Stromgren indices only in de-reddened form, but Plato field at moderate galactic latitude... Use ß–index, independent of reddening (same ). According to Crawford (AJ 80, 955) …again one notch on your error budget

Results • Error budget dominated by filter transformations (, ) because only two fields measured. Alleviated by slow variation in these coefficients. • Redding only significant in (b-y)

Teff (b-y) ,=0, inst=10mmag std=11.7mmag red=18.8mmag Sample data from Olsen, A&AS 57, 443

Metallicity (b-y,m1,c1) ,=0, inst=17.1mmag std=19.6mmag red=5.6mmag Sample data from Olsen, A&AS 57, 443

log(g) ,=0, inst=21.7mmag std=39.2mmag red=3.8mmag Sample data from Olsen, A&AS 57, 443

Conclusions • Extremely ambitious task. • Success depends on good filter transformation. • Are there enough standards (in the field)? • log(g) at best to distinguish dwarfs and giants. • Sacrifice filters/fields?

Getting Precise Stellar Parameters in PLATO’s first field